From edb839c803f4b0b991ec8d24a77d48bc5514029d Mon Sep 17 00:00:00 2001
From: Wilfred Hughes <me@wilfred.me.uk>
Date: Fri, 10 May 2024 16:26:48 -0700
Subject: [PATCH] Improve terminal width detection

Ensure the value is always non-zero, and consider $COLUMNS if
crossterm does not succeed.

Fixes #707
---
 CHANGELOG.md   |  8 ++++++++
 src/options.rs | 17 ++++++++++++++++-
 2 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 9c6374211d..4ffdb5794d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -29,6 +29,14 @@ Difftastic now has a man page, see the `difft.1` file.
 Fixed a memory leak and substantially improved performance in some
 cases (up to 2x in testing).
 
+### Command Line Interface
+
+Fixed a crash when difftastic could not detect the terminal width,
+such as inside eshell.
+
+Difftastic now also considers $COLUMNS when detecting the terminal
+width.
+
 ## 0.57 (released 1st April 2024)
 
 ### Parsing
diff --git a/src/options.rs b/src/options.rs
index daa156ee0e..774da35869 100644
--- a/src/options.rs
+++ b/src/options.rs
@@ -864,7 +864,22 @@ pub(crate) fn parse_args() -> Mode {
 /// to a sensible default value.
 fn detect_terminal_width() -> usize {
     if let Ok((columns, _rows)) = crossterm::terminal::size() {
-        return columns.into();
+        if columns > 0 {
+            return columns.into();
+        }
+    }
+
+    // If crossterm couldn't detect the terminal width, use the
+    // shell variable COLUMNS if it's set. This helps with terminals like eshell.
+    //
+    // https://github.com/Wilfred/difftastic/issues/707
+    // https://stackoverflow.com/a/48016366
+    if let Ok(columns_env_val) = std::env::var("COLUMNS") {
+        if let Ok(columns) = columns_env_val.parse::<usize>() {
+            if columns > 0 {
+                return columns;
+            }
+        }
     }
 
     DEFAULT_TERMINAL_WIDTH